Improving the performance of cell biocatalysis and the productivity of xylonic acid using a compressed oxygen supply

• An automatic oxygen supply method was put forward to improve cell catalysis performance of xylonic acid.
• 586.3 g/L xylonic acid was obtained from 600 g/L xylose.
• We could produce 143.9 g/L xylonic acid directly from crude lignocellulosic pre-hydrolysates.

Xylonic acid is useful and producing it in bacteria cost-effectively would be good because of potential applications and high yield. Production in bacteria like Gluconobacter oxydans is hampered by low xylose utilization and poor bacterial tolerance to contaminants. Here we exploited the oxygen-dependence of NAD+ regeneration and the lack of gas release during xylose metabolism in G. oxydans to develop a high-oxygen tension bioreactor with increased productivity. In this design we maintained gas outlets closed, which eliminated all bubbling and media foaming, and added a compressed pure oxygen inlet, which increased oxygen tension. Biocatalysis of xylose in this bioreactor yielded 3 times higher (586.3 g/L xylonic acid) than the best previous output. Moreover, we directly produced 143.9 g/L of xylonic acid from the diluted sulfuric acid pre-hydrolysates of corn stover without a detoxification process and at 1.0 g/L/h volumetric productivity. The central features of this bioreactor design are scalable and thus would enable cost-competitive bacterial xylonic acid production.